Manufacture of spark plugs



Sept. 19, 1933. G. M. PAULsoN MANUFACTURE 0F SPARK PLUGS original medJuly 15, 1929 3 wma. MIWMMZI J/ Patented Sept. 19, 1933 UNITED STATESPATENT OFFICE MANUFACTURE F SPARK PLUGS George M. Paulson, New York, N.Y., assignor to The B. G. Corporation, New York, N. Y., a corporation ofNew York i claim. (ci. asi-issn) This application is a division of mycopending application Serial No. 378,221, led July 15, 1929.

The present invention relates to spark plugs and the manufacture thereofand has particular reference to the manufacture of spark plugs intendedfor exceptionally severe service, such as aircraft motor plugs.

The service conditions imposed on plugs used in airplane motors isexceptionally severe, as the high compression ratios employed and theuse of air cooling result in extreme combustion chamber and cylindertemperatures, the effects of which the plugs must be able to withstand.Furthermore, plugs intended for this service must be formed to withstandextreme vibration and relatively sudden and wide temperature variationswithout the parts thereof tending to loosen. It is also desirable forplugs intended for such service to be of relatively compact form.

In accordance with the present invention l provide an improved method ofmanufacturing spark plugs by means of which plugs capable ofwithstanding the severe conditions of aircraft service above enumeratedmay be produced.

The method contemplated by the invention may be used in the manufactureof plugs of various kinds and types and its nature and the severaldetailed objects thereof may best be understood by a consideration ofthe following description of the several examples illustrated intheaccompanying drawing.

In the said drawing:

Fig. 1 is a Vertical section on an enlarged scale of a preferred form ofplug;

Fig. 2 is a section taken on the line 2 2 of Fig. 1;

Fig. 3 is a vertical section, enlarged, of another form of plug; and

Fig. 4 is a vertical section of a third form of plus.

Referring now to Fig. 1, the plug comprises a cylindrical centralspindle 1, preferably made from steel having a high heat-conductingcharacteristic, the upper portion of which is preferably corrugated by aseries of circumferential grooves 2 and the lower end of whichterminates in an enlarged semi-spherical head 3 from which the centerelectrode 4 projects. The head 3 is '50 preferably of specialnon-scaling steel welded to the spindle. and the electrode 4 of an alloysuch as manganese-nickel especially adapted to withstand erosion due tothe spark arc.

The spindle l is surrounded by a mica insulat- 5,5 ing tube 5, which itwill be noted extends for a e considerable distance above the upper endof the spindle. The lower end of the mica sleeve is surrounded by anumber ofl mica washers 6, which are held in place between the shoulderformed by the enlarged spindle head 3 and an annular cylindrical brasssleeve 7, the lower end of which is enlarged to form the conical portion7a.

The usual steel shell 8, threaded exteriorly at 9 and provided with asuitable electrode l0, is formed with a conical gasket seat 11, betweenwhich and the coupling nut 12 the soft copper 65 gasket 13 is placed toform a gas-tight seal. The lower conical portion 7a of sleeve 7 ts thecorrespondingly tapered bore 14 in nut 12, and the upper cylindricalportion of sleeve 7 is surrounded by the brass barrel 15. Barrel 15, itwill be noted, extends above the top of spindle 1, as do tube 5 andsleeve 7, the portion above the spindle having a smaller outer diameterthan that surrounding the spindle. A circumferential groove 16 islocated between the por- 75 tions of dilferent diameter.

The mica tube 5 is rolled on spindle 1, preferably with suicientpressure to cause it to press into grooves 2. Mica washers 6 are thenslipped over the tube, followed by sleeve 7, the latter being thenforced into the conical bore 14 of nut l2 with suiiicient force to forma tight joint. rlhe barrel 15 is then placed over the upper end ofsleeve 7 and an annular die drawn over the lower and larger diameteredportion of the barrel to compress it, and with it sleeve 7 and tube 5. Atremendous lateral pressure is thus exerted, forcing the insulation intothe spindle grooves and causing the metal in sleeve 7 and barrel l5 totake a permanent set which binds the several elements tightly andpermanently together. It will be apparent to those skilled in the artthat with a properly proportioned die, suicient lateral pressure may beexerted to bind the elements together without the aid of the spindlegrooves to prevent longitudinal movement.

In ordinary, or unshielded, spark-plugs, in which the-spindle extendsabove the top of the plug to receive a nut, it is simple to lock theparts in assembly. In the kind of spark-plug to which the presentinvention relates a more dicult problem is presented. It is essentialthat the parts of the plug remain in tight and solid assemblynotwithstanding the high temperatures and pressures and the great.vibration to which the spark-plugs are subjected in aviation enginesparticularly. The forces tending to cause slipping or loosening areespecially severe when the spindle is insulated in the highly effectiveman- 2. ner shown in the drawing, that is to say by mica wrapped aboutthe spindle and by a stack of mica discs held under compression betweenthe head of the spindle and a shoulder afforded by some part of what maybe termed the body of the spark-plug. This mica has-a relatively largecoeificient of expansion and when highly heated exerts a very greatforce tending to pull the spindle downward in the plug. This looseningforce is to be resisted without the aid of a top nut or the like, andthat is accomplished by providing for a tremendous inward compression ofa sleeve or barrel which extends above the upper end of the spindle, orof two metal elements surrounding the upper part of the spindle and itswrapped insulation. This permanent compression or distortion of themetal enclosure must extend over an appreciable length in order to beadequate as the sole locking of this assemblage. The portion compressedby a diedrawing operation should be cylindrical, or virtuallycylindrical, and should be of substantial length for effective results.

Other specific means for permanently deforming or setting the metal,such, for example, as a rolling operation, may be employed.

The assembly `thus formed results in a substantially integral unit, muchsuperior to corresponding units in prior known forms of plug, which insome instances have employed compressed metal rings to obtain agas-tight seal, but which have relied on threaded or equivalent meansfor holding the elements of the unit in assembled relation.

While in the preferred form illustrated, the nut 12 and barrel 15 areseparate elements, it will be understood that they may be made integralby welding, or from a single blank of the same metal heat-treated toform a hard lower threaded end and a relatively soft upper end suitablefor the die-drawing process above described.

In this particular form of plug, a brass elbow 17 lled with bakelite orother insulating material 18 is fitted over the upper end of barrel 15and held in place by the crimped end 19 fitting into the groove 16, thiscoupling, while holding the elbow against longitudinal displacement,permitting the elbow to be rotated about the axis of the barrel. Theconstruction of this elbow, the terminal connection and the meansproviding a path for high tension current to the spindle 1 need not bedescribed, as they form no part of the invention of this divisionalapplication.

In Fig. 3 a modified form of plug is shown in which the terminalconnection is axial with the plug. In this form the corrugated spindle 1is surrounded by the mica tube 5, which extends above the end of thespindle and is in turn surrounded by the sleeve 41, the lower conicalend of which is seated in the coupling nut 12. The upper end of sleeve41 has a lower larger diameter 42 and a smaller upper diameter 43.

In general, the assembly of this plug is similar to that of the formshown in Fig. l, sleeve 41 being set into nut 12 with sufficientpressure to assure a gas-tight seal. Spindle 1 and sleeve 5 are lockedin place by compressing the lower larger diametered portion 42 of sleeve41, preferably through a die-drawing operation, which will cause a flowof metal downward as well as inward to additionally insure a sealbetween sleeve 41 and nut 12. In this case sleeve 41 performs thefunction of barrel 15 shown in Fig. 1.

A brass cable terminal hub 45 is fitted tightly around the ignitioncable, the braided wire center 32 of which passes through a brass washer47, secured in place by a screw 48.

In Fig. 4, another variation is shown. In this form, the mica tube 5around spindle 1 is not extended above the upper end of the latter, andthe spindle and tube are set into the coupling nut 12 with a conicalbrass ring, which is sufficiently compressed to form a gas-tight seal.The coupling nut 12 is provided with an undercut recess 56 into whichthe lower end of brass sleeve 54 extends, this sleeve being lined with amica tube 55. Spindle 1 is locked in position by compressing sleeve 54,preferably by a die-drawing operation, which will cause the metal of thelatter to fiow into the recess 56. Alternately, sleeve 54 may beattached to nut 12 by rolling its lower end into the recess 56.

If the lower end of sleeve 54 is, as shown, smaller in diameter than theshouldered portion 44, a split die may be used for the drawingoperation.

From the foregoing description it will be seen that the presentinvention provides a form of plug which meets the severe conditionsimposed on plugs in the class of service for whch it is intended, as theconstruction according to the invention provides a mica-insulatedhigh-tension unit which is, after assembly, substantially integral andtherefore not subject to the possibility of loosening or disassembly dueto backing off of nuts because of motor vibration, as in the case withheretofore known forms of mica plugs.

The improvement of this invention relates more especially to spark-plugsof the shielded type, in which the high-tension current carryingelements of the system are entirely surrounded by a metallic shieldgrounded to the motor, to absorb the high frequency discharges whichwould affect reception of signals in an adjacent radio receiving set,such shield also serving as a protection against short-circuiting of thehigh-tension current by moisture from rain, snow or sleet, or bydeposits of oil thrown from the engine or of salt from sea spray. Theshielding of the plug is fully described in the application of whichthis is a division.

I claim:

In the manufacture of spark-plugs. the method which consists insurrounding the spindle with a mica insulating sleeve, providing as partof the outer structure of the plug a substantially cylindrical sleeve orbarrel that surrounds the spindle and insulating sleeve and extendsabove the upper end of the spindle, and, by temporarily applying forcearound said cylindrical sleeve and lengthwise thereof, creating a broadzone of permanent and distributed compression capable of locking thespindle in the spark-plug, in the absence of other aid, without injuryto the insulating sleeve.

GEORGE M. PAULSON.

